Lighting apparatus

ABSTRACT

A lighting apparatus is provided which illuminates a two dimensional data reading area in a data reader and which includes a plurality of light sources which are arranged along one pair of opposing sides of the two dimensional data reading area. An optical axis for each of the light sources is inclined at a predetermined inclination angle with respect to a line that is normal to a reference surface of the data reading area. The optical axes of the light rays emitted from the light sources onto the reference surface are spaced from the pair of sides of the two dimensional data reading area, at a distance within a range of 0.1 to 0.34 times the length of the other pair of opposing sides of the two dimensional data reading area.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lighting apparatus which is mounted,for example, to a data reader which reads coded data such astwo-dimensional data symbols.

2. Description of the Related Art

In a known POS (Point-of-Sale) system, a bar code reader (opticalscanner) reads a bar code which represents sales data. The bar codewhich is in the form of a series of lines of varying width is scannedperpendicular to the direction in which the lines were drawn, by laserbeams. However, not much data can be obtained from the bar code usingthis one-dimensional scanning method.

In order to provide much more data, a two-dimensional data symbolconsisting of a two-dimensional matrix (mosaic pattern) of, for example,white and black segments has been recently proposed and used. However,there are few simple data readers available, particularly those kindsusing an area sensor to read the two-dimensional data symbols.

In order to simultaneously read two-dimensional data symbols placed inorthogonal directions within a plane, it is necessary to uniformlyilluminate the two-dimensional data symbols in the orthogonaldirections. Accordingly, if a conventional lighting apparatus, which hasbeen used for a data reader for one-dimensional data symbols touniformly illuminate the latter only in one direction, is used for thetwo dimensional symbol data, it is impossible to uniformly illuminatethe latter in the orthogonal directions. Hence, in an attempt to developa data reader for two-dimensional data symbols, it is necessary torealize a lighting apparatus which can simultaneously and uniformlyilluminate two-dimensional data symbols within a data reading area whichis drawn on a single plane.

Furthermore, if the light emitted from the light source is reflectedwithin the data reading area and reaches the CCD, a spurious image ofthe light source is formed on the CCD, thus resulting in a failure tocorrectly read the data.

To solve these problems, it is necessary to provide an appropriate anglebetween the optical axis of the illumination light and a line normal toa reference surface on which the two-dimensional data symbols are formedwithin the data reading area.

However, if there is a large angle of inclination of the optical axis ofthe illumination light with respect to the normal line to the referencesurface, the lateral size of the lighting apparatus is increased,leading to a large data reading apparatus.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide a small datasymbol reading apparatus in which two-dimensional data symbols within adata reading area can be uniformly illuminated and can be correctlyread, regardless of the state of the reference surface of the datareading area.

To achieve the object mentioned above, according to the presentinvention, a lighting apparatus which illuminates a two dimensional datareading area in a data reader is provided. The lighting apparatusincludes a plurality of light sources arranged along one pair ofopposing sides of the two dimensional data reading area, and an opticalaxis for each light source being inclined at a predetermined inclinationangle with respect to a line normal to a reference surface whichincludes the two dimensional data reading area.

According to another aspect of the present invention, a lightingapparatus which illuminates a two dimensional data reading area in adata reader is provided. The lighting apparatus includes a plurality oflight sources arranged along one pair of sides of the two dimensionaldata reading area, and an optical axis is provided for each said lightsource being inclined at a predetermined inclination angle with respectto a line normal to a reference surface which includes the data readingarea. The optical axes of light rays emitted from the light sources ontothe reference surface are spaced from one pair of the sides of the twodimensional data reading area at a distance between a range of 0.1 to0.34 times the length of the other pair of opposing sides of said twodimensional data reading side.

According to the another aspect of the present invention, a lightingapparatus which illuminates a rectangular data reading area in a datareader Is provided, which includes a plurality of light sources whichemit light beams to illuminate the rectangular data reading area. Anadjuster if provided for each of the light sources which adjusts theluminance of the light source at a center point of illumination of thelight source incident on a reference surface which includes the datareading area, to thereby uniformly illuminating the data reading area.

According to the another aspect of the present invention, a data symbolreading apparatus for reading a plurality of two dimensional datasymbols is provided, which includes a light source for illuminating adata reading area. The data reader area receives a light reflected fromthe data reading area, and a light guiding optical system is providedwhich has a mechanism deflect the light emitted from the light sourcesuch that the light emitted from the light source is incident upon adata reading area. An optical axis of the light source is inclined at apredetermined inclination angle with respect to a line normal to thedata reading area.

According to the still another aspect of the present invention, a datasymbol reading apparatus for reading two-dimensional data symbols inprovided, which includes a light source for illuminating a data readingarea, a data reader area which receives a light reflected from the datareading area, and a prism which is provided with a reflecting surfaceand an emitting surface and which deflects a light emitted from thelight source to make the light incident upon a reference surface of thedata reading portion. The prism is provided on the emitting surface witha plurality of V-shaped grooves, that are arranged in a direction of aline normal to the light receiving surface of the data reader area.

The present disclosure relates to subject matter contained in Japanesepatent application Nos. 05-249897 (filed on Sep. 9, 1993), 05-256468(filed on Sep. 20, 1993), 05-261845 (filed on Sep. 24, 1993), and06-87818 (filed on Apr. 1, 1994) which are expressly incorporated hereinby reference in their entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below in detail with reference to theaccompanying drawings, in which;

FIG. 1 is a schematic side sectional view of a data reader according tothe present invention;

FIG. 2 is a schematic isometric view of a lighting apparatus and a datareading portion, according to the first three embodiments of the presentinvention;

FIG. 3 is a plan view of a symbol reading area, by way of example;

FIG. 4 is a plan view of illuminating points by a light source within adata reading area;

FIG. 5 is an explanatory view of an illumination angle of light emittedfrom a light source onto a data reading area;

FIG. 6 is a graph of an orientation characteristic curve of a lightsource (light emitting diode);

FIG. 7 is a block diagram of a circuit in a data reader;

FIGS. 8a and 8b are diagrams of a first example of a luminancedistribution on a data reading area of a data reader, in a majordirection and a minor direction, respectively;

FIGS. 9a and 9b are diagrams of a second example of a luminancedistribution on a data reading area of a data reader, in a majordirection and a minor direction, respectively;

FIGS. 10a and 10b are diagrams of a third example of a luminancedistribution on a data reading area of a data reader, in a majordirection and a minor direction, according to a third embodiment of thepresent invention, respectively;

FIGS. 11a and 11b are diagrams of a comparative example of a luminancedistribution on a data reading area of a data reader, in a majordirection and a minor direction, respectively;

FIGS. 12a and 12b are diagrams of another comparative example of aluminance distribution on a data reading area of a data reader, in amajor direction and a minor direction, respectively;

FIG. 13 is a schematic isometric view of a lighting apparatus and a datareading portion, according to a fourth embodiment of the presentinvention;

FIG. 14 is a schematic isometric view of a lighting apparatus and a datareading portion, according to a fifth embodiment of the presentinvention;

FIG. 15 is a schematic perspective view of a lighting apparatus and adata reading portion, according to sixth and seventh embodiments of thepresent invention;

FIG. 16a is a diagram of a comparative example of the luminancedistribution on a data reading area of a data reader;

FIG. 16b is a diagram of an example of a luminance distribution on adata reading area of a data reader, according to the present invention;

FIG. 17 is a schematic side sectional view of a data symbol readeraccording to the present invention;

FIG. 18 is a schematic isometric view of a lighting apparatus and a datareading portion, according to an eighth embodiment of the presentinvention;

FIG. 19 is a schematic side elevational view of a lighting apparatus anda data reading portion, according to the eighth embodiment of thepresent invention;

FIG. 20 is a schematic side elevational view of a lighting-apparatus anda data reading portion, according to ninth embodiment of the presentinvention;

FIG. 21 is an enlarged side elevational view of optical paths of beamspassing through prisms for the lighting apparatus shown in FIG. 20;

FIG. 22 is a schematic side elevational view of a lighting apparatus anda data reading portion, according to a tenth embodiment of the presentinvention;

FIG. 23 is a schematic side sectional view of a data symbol readeraccording to the present invention;

FIG. 24 is a plan view of a symbol reading area, by way of example;

FIG. 25 is a schematic side elevational view of a lighting apparatus anda data reading portion, according to the present invention;

FIG. 26 is a side elevational view of a prism according to the presentinvention, by way of example;

FIG. 27 is a side elevational view of opposed prisms according to thepresent invention, by way of example;

FIG. 28 is a graph of a luminance distribution of a data reading area ina horizontal direction (minor side direction), according to the presentinvention;

FIG. 29 is a graph of a illumination distribution of a data reading areain a horizontal direction (minor side direction), according to thepresent invention; and,

FIG. 30 is a side elevational view of opposed prisms having no grooveson the emitting surfaces thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 schematically shows an internal structure of a portable datareader 1, which includes a casing 2, which integrally provides alighting apparatus 40 and a data reader 4 which reads a data symbol 38.

The lighting apparatus 40 is provided with two arrays of light sources45 and 46 on opposed sides of the data reader 4. The lighting apparatus40 is connected to a light source driving circuit 42 which activateslight emitters 41, including a light emitting element such as an LED, ahalogen lamp, or a semiconductor laser, etc.

The data reader 4 which is provided between the light source arrays 41is comprised of a CCD (charge coupled device) sensor 43 (an area sensor)and an optical system 44 which converges light reflected from the datareading area 36, which will be discussed hereinafter, onto the CCDsensor 43. The CCD sensor 43 includes a number of picture elements(pixels) in a matrix arrangement within a light receiving area, so thatthe picture elements accumulate electric charges corresponding to theluminous energy received. The electric charges are sent to and read by asignal processing circuit 5 at a predetermined time. The electriccharges read constitute two-dimensional signals corresponding to thelight receiving area.

In the illustrated embodiment, the CCD sensor 43 can be of any type thatdetects the brightness (luminance) of each part of the data symbol 38.Depending on the structure of the data symbol to be read, a CCD sensorfor a color image can be used.

The optical system 44 is comprised of optical elements in combination,such as lens(es), prism(s), filter(s), and/or mirror(s), etc.

FIG. 3 shows an example of a data (symbol) reading area 36 in plan view.As can be seen in FIG. 3, the data reading area 36 indicated by a dottedand dashed line defines an area of a reference surface 37 (on which thedata symbol 38 lies) that is illuminated with light from the lightingapparatus 40, so that the light reflected thereby can be received by thedata reader 4 to read data represented by the symbol 38. For example, ifa general-purpose CCD sensor is used, the data reading area 36 is in theform of a rectangle of 4×3.

In the illustrated embodiment, the data symbol (symbol code) 38 forms amosaic pattern of black and white (or transparent) segments in a matrixarrangement of x (row)x y (column), wherein x and y are integers equalto or more than 2. The black and white segments represent "0" or "1",for example, in a binary number system. Consequently, desiredinformation is represented by a combination of "0" and "1". Note thatthe data symbol 38 is not limited to the illustrated embodiment.

With the arrangement of the lighting apparatus 40 and the data reader 4as constructed above, when the light sources 41 are turned ON by thelight source driving circuit 42, the beams emitted from the lightsources 41 are made incident upon the data reading area 36, so that thelight reflected thereby can be received by the light receiving surfaceof the CCD 43 through the optical system. Hence, the CCD 43 outputsimage signals (analog signals) corresponding to the quantity of light(luminous energy) to be received.

The lighting apparatus 40 will be discussed below in detail withreference to FIG. 2. The lighting apparatus 40 is comprised of aplurality of light source arrays 45 and 46, and optical diffusionsystems 47 and 48 provided between the respective light source arrays 45and 46 and the data reading area 36.

The light source arrays 45 and 46 are each provided with two lightemitting elements (light sources) 41. It is possible to provide morethan two light emitting elements 41 in each light source array 45 or 46.

The light source arrays 45 and 46 are located above and along the majorsides of the data reading area 36 in a data reading position. Althoughthe diffusion systems 47 and 48 are made of diffusion plates havingdiffusion surfaces in the illustrated embodiment, the diffusion systems47 and 48 can be made of, for example, cylindrical lenses.Alternatively, if light sources having a weak direction determiningcapability are used, the diffusion systems can be eliminated.

The illumination direction of the light emitters 41 is such that thebeams are emitted thereby inward from the outside of the data readingarea 36 in oblique directions. Namely, in a plan view shown in FIG. 4,the optical axes of the light emitted from the respective light emitters41 are parallel with and normal to the minor sides and the major sidesof the rectangular data reading area 36, respectively. Also, in a sideview of the data reading area 36 viewed from one of the minor sidesthereof, as shown in FIG. 5, the beams are incident upon the datareading area 36 at an incident angle 6 with respect to the line normalto the reference surface 37.

In the illustrated embodiment, the incident angle θ is 30° to 60°,preferably, 40° to 50°, and most preferably, 43° to 48°. If the incidentangle is smaller than the lower limit (30°), the beams are extremelyconcentrated at the center point P of illumination, so that the datareading area 36 can not be sufficiently illuminated, thus resulting inan irregular degree of brightness. Furthermore, the directly reflectedlight component is increased, so that spurious images of the lightsources occur, causing reading errors. Conversely, if the incident angleis above the upper limit (60°), there is an increase in the variation ofthe brightness in the major side direction of the data readingrectangular area (i.e., the direction of the arrays).

The light sources (light emitters) 41 have a substantially identicalluminance and a substantially identical orientation property. The lightsources 41 that constitute the same array 45 or 46 are oriented in thesame direction so as to have parallel optical axes. FIG. 4 shows thelight data reading area 36 illuminated by four light sources 41 as inthe illustrated embodiment. The centers of the incident light sources onthe data reading area are marked "P". Lines drawn in the minor and majordirections connecting the points P ere indicated as "n" and "q"respectively. "n" and "q" are parallel to the minor and major sidesrespectively. The lines "q" are between the median line "my" of the datareading area 36 and the respective major sides, parallel with the majorsides thereof and are closer to the respective major sides than to themedian line "my". The lines "n" are between the median line "mx" of thedata reading area 36 and the respective major sides, parallel with theminor sides thereof and are closer to the respective minor sides than tothe median line "mx".

In the illustrated embodiment, the positions of the lines "q" and "n"are respectively defined by;

    Δ Lx=α Lx, Δ Ly=β Ly

wherein "Lx" designates the length of the minor sides, "Ly" the distancebetween the lines "q" and the corresponding major sides, "Δ Ly" thedistance between the lines "n" and the corresponding minor sides,respectively.

The value of α is approximately 0.1 to 0.34, and preferably 0.15 to0.22. If the value of α is smaller than 0.1, the center portion of thedata reading area 36 tends to be dark. If the value of α is larger than0.34, the edge portions of the data reading area 36 in the vicinity ofthe major sides thereof are dark, resulting in a non-uniformillumination of the entire data reading area 36.

The value of β is approximately 0.1 to 0.25, and preferably 0.1 to 0.2.If the value of β is smaller than 0.1, the center portion of the datareading area 36 tends to be dark. If the value of β is larger than 0.25,the edge portions of the data reading area 36 in the vicinity of themajor sides thereof are dark, resulting in a non-uniform illumination ofthe data reading area 36.

The light sources 41 preferably have an identical luminance. Theorientation property of the light sources 41 is shown in FIG. 6 by wayof example.

In the illustrated embodiment, the light sources (light emitters) 41 aredisposed in a symmetrical arrangement with respect to a planeperpendicular to the reference surface 37, including the median line"my". The center points P of illumination are disposed in a symmetricalarrangement with respect to the median lines "mx" and "my",respectively.

When the beams emitted from the light sources 41 are transmitted throughthe diffusion systems 47 and 48, the beams are diffused to illuminate apredetermined zone of the data reading area 36. Since the optical axesof the beams are inclined toward the major sides along the minor sides,with respect to the reference surface 37, the beams are diffused towardthe median line "my" of the data reading area 36 from the optical axes.The diffused lights from the opposed light sources are overlapped on themedian line "my", so that the luminance at the median line "my" or inthe vicinity thereof is substantially the same as the luminance at thecenter points P of illumination, thus resulting in a uniform brightnessover the whole data reading area 36.

It is not necessary for the direction of the beams emitted from thelight sources to be parallel with the minor sides of the data readingarea, as shown in FIG. 4. Namely, the beams can be emitted inward fromthe outside of the minor sides in oblique directions by the lightsources to be parallel with the major sides.

As can be seen in FIG. 7, the signal processing circuit 5 essentiallyincludes a CCD driving circuit 6, an amplifier circuit 8, a binary codecircuit 10, a memory 12, a control means (CPU) 15, a communicatingdriver 16, and lines connecting these elements.

A light source driving circuit 42, a switch circuit and/or a displaysuch as LCD (Liquid Crystal Display), not shown are connected to thecontrol means 15, in accordance with need.

The data is read by the data symbol reader 1 when a trigger switch istuned ON. The signals processed by the signal processing circuit 5 aredecoded into desired data and then inputted to an external computer,such as a personal computer or a work station through the communicatingdriver 16. The data inputted into the computer 17 is stored and summed.

The light source driving circuit 42 supplies the light sources 41 withthe electrical power to activate the same to thereby emit the beams inaccordance with the control of the control mechanism 15. When a mainswitch (not shown) is actuated, the control mechanism 15 actuates thelight source driving circuit 42 to thereby turn the light sources 41 ON.The time in which the light sources 41 are activated is selected to be apredetermined value by the light source driving circuit 42 or thecontrol mechanism 15.

Also, when the main swatch is turned ON, the control mechanism 15actuates the CCD driving circuit 6. Horizontal driving pulses andvertical driving pulses are outputted from the CCD driving circuit 6 tothe CCD 43 to control the accumulation and transfer of the electriccharges in the CCD 43.

The CCD driving circuit 6 generates clock signals and outputs compositesignals (composite clock signals) of the clock signals and horizontaland vertical synchronization signals to the control mechanism 15.

The image signals (analog signals) for each picture element,successively outputted from the CCD 43 of the data reading portion 4 areamplified by the amplifier circuit 8 and converted to digital signalswhich are then inputted to the binary code circuit 10.

The digital image signal corresponding to each picture element iscompared with threshold data and converted to binary data in the binarycode circuit 10. The binary data obtained are inputted into the memory12 at a predetermined address through the address counter incorporatedin the control mechanism 15. The address counter is driven in accordancewith the composite clock signals inputted thereto from the CCD drivingcircuit 6.

The data stored in the memory 12 is successively read in accordance withdesignated addresses in the built-in address counter, so that thecalculating portion of the control mechanism 15 carries out theprocessing of the image data for one picture plane, such as a detectionof the profile (selection of data on the data symbols 38 only), acorrection of a dropout error, or the rotation, etc. The processed datais then decoded into data corresponding to the system of the datasymbols by a decoder incorporated in the control mechanism 15. Thedecoded data is outputted to a host computer 17 through thecommunicating driver 16.

Furthermore, the present invention is not limited to the illustratedembodiments. The present invention can be applied to a different size ofrectangular data reading area. The rectangular data reading areareferred to herein includes a square data reading area. Moreover, themajor sides and the minor sides of the rectangular data reading area inthe illustrated embodiment can be interchanged.

Several examples of the luminance distribution will be discussed below.

The luminance distributions of the data reading area were measured usingthe lighting apparatus shown in FIG. 2. The four light emitting diodesused as the light sources were identical to each other. Theirorientation property is shown in FIG. 6. The size of the data readingarea was as follows; Lx=18.5 mm and Ly=24.5 mm.

Other experimental conditions in the examples are described below.

FIGS. 8a through 12b show examples of luminance distribution of the datareading area 36 (FIG. 3) which is illuminated with the beams emittedfrom the light sources according to the present invention. The ordinaterepresents the level of the video signals (unit: IRE), and the abscissarepresents the position of the illumination points on the median linesor the lines mentioned above, respectively.

In FIGS. 8a through 12b, the upper curves show luminance distributionsfor the lines "q" and "n" which connect the center points P of eachillumination, and the lower curves show luminance distributions on themedian lines "mx" and "my", respectively. FIGS. 8a, 9a, 10a, 11a and 12ashow the luminance distributions of the data reading area 36 in themajor side direction (horizontal direction) thereof, end FIGS. 8b, 9b,10b, 11b and 12b show the luminance distributions of the data readingarea 36 in the minor side direction (vertical direction) thereof,respectively. It should be appreciated that the uniformity ofillumination over the data reading area 36 is improved as the distancebetween the upper and lower curves decreases and the curves become morestraight.

EXAMPLE 1:

Center points P of illumination: Δ Lx=0.2Lx, Δ Ly=0.2Ly

Incident anglesθ: 40°

EXAMPLE 2:

Center points P of illumination: Δ Lx=0.2Lx, Δ Ly=0.2Ly

Incident angleθ: 50°

EXAMPLE 3:

Center points P of illumination: Δ Lx=0.2Lx, Δ Ly=0.2Ly

Incident angleθ: 45°

Comparative Example A:

Center points P of illumination: Δ Lx=0 (i.e., the center points P ofillumination are located on the major sides of the rectangular datareading area), Δ Ly=0.2Ly

Incident angle θ: 45°

Comparative Example B:

Center points P of illumination: Δ Lx=0.35 Lx, Δ Ly=0.2Ly

Incident angle θ: 45°

As can be seen from the experimental results mentioned above, in example1, there was only a small difference in the brightness between the lines"q", "n" and the corresponding median lines, and the difference in theluminance between the brightest portion and the darkest portion wasabout 10IRE. Also, in the example 2 shown in FIGS. 9a and 9b, thedifference in the luminance between the brightest portion and thedarkest portion was about 10IRE. Consequently, in examples 1 and 2, asubstantially uniform brightness over the whole area was obtained.

In example 3 shown in FIGS. 10a and 10b, there was little difference inthe brightness between the lines "p", "n" and the corresponding medianlines, and there was little difference in the luminance between thelines "p" and "n".

Looking at the comparative example A shown in FIGS. 11a and 11b, theluminance distribution is such that the center portions are dark and thedifference in the brightness between the dark portion and the brightportion is around 20IRE. Also, in the comparative example B shown inFIGS. 12a and 12b, the center portions and the edge portions are dark,and the difference in the brightness between the dark portion and thebright portion is approximately 20IRE. Consequently, it can beappreciated that a non-uniform illumination is obtained in thecomparative examples A and B.

It was experimentally confirmed that the same results as the foregoingwere obtained when the values of Δ Ly were replaced with 0.15Ly and0.25Ly, respectively.

As can be understood from the above discussion, according to the presentinvention, the data reading area can be uniformly illuminated, tothereby correctly read the coded data. In particular, according to thepresent invention, the data reading area is not limited to beingilluminated by only four light sources.

FIGS. 13 through 16 show other embodiments of the present invention. Inthe illustrated embodiment, each of the arrays 245 and 246 is providedwith three light sources 241a₁, 241b and 241a₂. The light source arrays245 and 246 are located above and along the major sides of the datareading area 36 in a data reading position. Although the diffusionsystems are made of diffusion plates 247 and 248 having diffusionsurfaces in the illustrated embodiment, the diffusion systems can bemade, for example, of cylindrical lenses. Alternatively, if lightsources having a weak direction determining capability are used, thediffusion systems can be dispensed. The directional property of thelight sources 241a₁, 241b, and 241a₂ is shown in FIG. 6.

The optical axes 249a₁, 249b and 249a₂ of the light sources 41a₁, 241band 241a₂ which constitute the respective arrays 245 and 246 areparallel. Imaginary planes including the optical axes 249a₁, 249b and249a₂ intersect the reference surface 37 of the data reading area 36 ata predetermined inclination angle. The intersection lines of theimaginary planes and the reference surface 37 are parallel with themajor sides of the data reading area 36. The imaginary planes areinclined to increase the distance therebetween and the CCD 43.

The angle defined by the imaginary planes including the optical axes249a₁, 249b and 249a₂ and the reference surface 37 is 30° to 60°, andpreferably, 40° to 50°. When the angle is within this range, thereference surface 37 can be uniformly illuminated with the beams emittedfrom the lighting apparatus according to the present invention.

The intersection lines "q" formed by the intersection between theimaginary light planes and the reference surface 37 are parallel withthe major sides of the rectangular data reading area 36 and the medianline "my" of the minor sides of the data reading area 36. Furthermore,the optical axes 249a₁, 249b and 249a₂ intersect the lines "q" at rightangles. The intersection points Pa₁, Pb and Pa₂ of the optical axes249a, 249b and 249a₂ and the intersection lines "q" constitute thecenter points of illumination by the beams emitted from the respectivelight sources. In the arrangement of the light sources having theorientation property as mentioned above, the maximum luminance isobtained at the center points Pa₁, Pb and Pa₂ of illumination, on theassumption that the reference surface 37 is illuminated one at a time byone of the light sources.

When the beams emitted from the light sources 241 are transmittedthrough the diffusion plates 247 and 246, the beams are diffused toilluminate a predetermined zone of the data reading area 36.

The luminances of the light sources 241a₁, 241b and 241a₂ thatconstitute each array 245 or 246 are such that the luminances of theouter light sources 241a₁ and 241a₂ are identical to each other andlarger (brighter) than the luminance of the intermediate light source241b.

If the beams are emitted individually by only the light source 241a₁ thelight source 241b or the light source 241a₂, then the luminance on thereference surface 37 at the center points Pa₁ & Pa₂ of illuminationwould be larger than the luminance on the reference surface 37 at thecenter point Pb of illumination. Namely, the center points Pa₁ & Pa₂ ofillumination are brighter than the center point Pb of illumination forthe case where the beams are emitted individually. If all the lightsources 241 are activated together, the beams emitted from the outerlight sources 241a₁ and 241a₂ are diffused by the correspondingdiffusion plates so as to illuminate a large area of the data readingarea 36, from the edge portions to the center portions including thecenter points Pb of illumination. Consequently, the whole data readingarea along the lines "q" can be uniformly illuminated. The same is truefor the data reading area, for example, along the median line "my"parallel with the lines "q". Thus, the entirety of the data reading areacan be uniformly illuminated.

If each of the arrays 245 and 246 is comprised of more than three lightsources 241, the luminance of the outermost light sources is higher thanthe luminance of the inner light sources, so that the data reading areacan be uniformly illuminated. If the light sources 241 of each array arespaced et a substantially equi-distance, it is preferable that theoutermost light sources have an identical high luminance and the innerlight sources have an identical low luminance. Preferably, the centerpoints P of illumination are located in a symmetrical arrangement withrespect to the median line "my".

Light sources having different fixed luminances or variable luminances(that can be varied by the control of the driving voltage appliedthereto) can be used. Namely, in the latter case, the driving voltage tobe applied to light sources whose luminance must be high is increasedand the driving voltage to be applied to the light sources whoseluminances must be low is decreased, respectively. In the illustratedembodiment, the driving voltage to be applied to the light sources 241bis selected to be lower than that to be applied to the light sources241a₁ and 241a₂, so that the light intensity of the light sources 241bcan be reduced without changing the orientation property.

The lines "q" are spaced at a distance Δ L in the minor side directionfrom the major sides of the rectangular data reading area, as shown inFIG. 13. The value of Δ L is within the range of 0.1 to 0.34 times, andpreferably, 0.15 to 0.25 times the length of the minor sides, so thatthe reference surface 37 of the data reading area 36 can be uniformlyand two-dimensionally illuminated.

In the fifth embodiment shown in FIG. 14, the inner light source 241b ineach array 245 or 246 that includes a plurality of light sources islocated farther from the data reading surface 36 than the outer lightsources 241a₁ and 241a₂. Namely, the distance of the light sources 241bfrom the data reading area 36 is longer than the distance of the lightsources 241a₁ and 241a₂ from the data reading area 36. With thisarrangement, the luminance at the center points Pb of illumination or inthe vicinity thereof, illuminated by light emitted from the lightsources 241b is smaller than the luminance at the center points Pa ofillumination or in the vicinity thereof, illuminated by light emittedfrom the light sources 241a₁ and 241a₂.

In a sixth embodiment illustrated in FIG. 15, the separate diffusionplates 247 and 248 are provided for the respective light sources 241.Namely, there are diffusion plates 247a₁, 247b and 247a₂ correspondingto the light sources 241a₁, 241b and 241a₂ of the light source array 245and diffusion plates 248a₁, 248b and 248a₂ corresponding to the lightsources 241a₁, 241b and 241a₂ of the light source array 246,respectively. The inner diffusion plates 247b and 248b have adiffusability different from that of the outer diffusion plates 247a and248a. In the illustrated embodiment, the intermediate diffusion plates247b and 248b have a higher diffusability than the diffusability of theouter diffusion plates 247a and 248a, so that the luminance of lightemitted by the light sources 241b is lower than that by the lightsources 241a₁ and 241a₂.

In a modified (seventh) embodiment, it is possible to provide opticalfilters that constitute a beam attenuating mechanism in the opticalpaths of the light sources 241b to attenuate the quantity of the beamsreaching the center points Pb of illumination.

In the fifth, sixth and seventh embodiments mentioned above, all thelight sources to be used can be of an identical type.

Several examples of the luminance distribution will be discussed below.

The luminance distributions of the data reading area were measured,using the fourth embodiment of the lighting apparatus shown in FIG. 13.The six light emitting diodes used as the light sources were identicalto each other, The orientation property thereof is shown in FIG. 6. Thesize of the data reading area was as follows; Lx(minor sides)=18.5 mm,and Ly(major sides)=24.5 mm.

Other experimental conditions in the examples were described below.

FIGS. 16a and 16b show examples of luminance distribution of the datareading area 36 (FIG. 3) which is illuminated with the beams emittedfrom the light sources according to the present invention. The ordinaterepresents the level of the video signals (unit: IRE), and the abscissarepresents the position of the illumination points on the lines "q"mentioned above, respectively. The center points P of illumination weresuch that the distance L₁ between the minor sides of the data readingarea 36 and the center points Pa of illumination and the distance L₂between the center points Pa of illumination and the center points Pb ofillumination satisfy the relationship defined by (L₁ : L₂ =5:7).

The distance of the center points Pa₁, Pb and Pa₂ of illumination fromthe major sides of the data reading area 36 were 0.2 times that lengthof the minor sides and the angle of the optical axes of the lightsources 241 with respect to the normal line to the reference surface 37was 45°.

The curves in FIGS. 16a and 16b show the luminance distribution on thelines "q". It should be appreciated that the uniformity of illuminationover the data reading area 36 is improved as the curves becomeapproximately straight lines.

Comparative Example C:

The luminance of the light sources 241b was identical to the luminanceof the light sources 241a₁ and 241a₂. The luminance at the center pointsPb of illumination when only the light sources 241b were activated wasidentical to the luminance at the center points Pa of illumination whenonly the associated light sources 241a₁ and 241a₂ were activated. Theresults are shown in FIG. 16a.

EXAMPLE 4:

A resistor was inserted in an output line of the light source drivingcircuit to reduce the driving voltage of the light sources 241b, so thatthe luminance of the light sources 241b were lower than the luminance ofthe remaining light sources 241a₁ and 241a₂. The luminance at the centerpoints Pb of illumination when only the light sources 241b wereactivated was smaller, by approximately 17%, than the luminance at thecenter points Pa of illumination when only the associated light sources241a₁ and 241a₂ were activated. The results are shown in FIG. 16b.

As can be seen in FIG. 16a, in the comparative example, the luminance atthe center portion of the data reading area is higher than that at theperipheral portion. The difference e₁ in the luminance between thebright portion and the dark portion in the comparative example shown inFIG. 16a is larger than the corresponding difference e₁ in the example 1shown in FIG. 16b. Namely, the lines "q" on the data reading area 36 canbe more uniformly illuminated in the present invention than in thecomparative example. It was experimentally found that the difference inthe luminance on the median lines "mx" (in the minor side direction)perpendicular to the lines "q" was smaller than the above-mentioneddifference e₂ in the major side direction.

EXAMPLE 5:

The light sources having an identical luminance and optical axesinclined with respect to the reference surface at the same inclinationangle as that in example 4 mentioned above were used. The light sources241b were located farther from the reference surface 37 than the otherlight sources 241a₁ and 241a₂ to reduce the luminance at the centerpoints Pb in order to give substantially the same luminance at the datareading surface 36 to be identical to the luminance in example 4.Substantially the same results as those in example 4 were obtained.

EXAMPLE 6:

The diffusion plates were separately provided with separate lightsources. The difffusability of the diffusion plates 247b and 248b of thelight sources 241b was larger than the diffusability of the remainingdiffusion plates to reduce the luminance at the center points Pb inorder to give substantially the same luminance at the data readingsurface 36 as in example 4. Consequently, substantially the same resultsas in example 4 were obtained.

EXAMPLE 7:

Filters were provided between the light sources 241b and the referencesurface 37 to attenuate the quantity of light from the light sources241b, so that the luminance at the center points Pb would givesubstantially the same luminance as in example 4. Consequently,substantially the same results as in example 4 were obtained.

As can be understood from the foregoing, according to the presentinvention, the two-dimensional symbols in a data reading area can beuniformly illuminated, to allow the coded data to be read correctly.

The data reading area can be more uniformly illuminated by theinclination of the optical axes of the light sources with respect to thereference surface of the data reading area and by the location of thecenter points of illumination spaced at a predetermined distance fromthe minor sides of the rectangular data reading area.

The eighth embodiment of the lighting apparatus according to the presentinvention will be described below with reference to FIGS. 18 and 19. Thelighting apparatus 340 includes a plurality of light sources 341,diffusion plates 347 which constitute an optical diffusion system, andshading plates 348 which constitute a shading means.

In the illustrated embodiment, there are, on the opposed sides of theCCD 343, two arrays 345, each having two light sources 341. Only one ofthe arrays 345 is shown in FIG. 18. The CCD 43 is provided with a lightreceiving surface perpendicular to a line O normal to the referencesurface 37 of the data (symbol) reading area The optical axis of thelight incident upon the CCD 43 is parallel with the normal line O. Thelight sources 341 are arranged such that the optical axis of the lightthat has been emitted from the light sources 341 but has not yet reachedthe guiding optical system is substantially parallel with the opticalaxis of the light incident upon the CCD 43, and accordingly, the line tothe reference surface 37 (i.e., α≈0).

The arrays 345 are located along a pair of opposed parallel sides (majorsides in the illustrated embodiment) of the rectangular data readingarea 36. The mirrors 346 are provided in the optical paths of the lightof emitted from the light sources 341 and along the major sides of thedata reading area 36.

There are diffusion plates 347 between the light sources 341 and themirrors 346. Shading plates 348 are provided below the diffusion plates347 on the side adjacent to the data reading area 36. The shading plates348 prevent the light emitted from the light sources 341 from beingdirectly made incident upon the data reading area 36.

When the beams emitted from the light sources are transmitted throughthe diffusion plates 347, the beams are diffused so as to illuminate alarge area of the data reading area 36 and make the luminancesubstantially constant within the illumination range.

The surfaces of the shading plates 348 facing the mirrors 346 can bemirror surfaces. In this case, the beams are reflected by the mirrorsurfaces of the shading plates 348 and by the mirrors 346 toward thedata reading area 36. Consequently, no attenuation of the brightness dueto the partial absorption of the beams by the shading plates occurs,resulting in an effective utilization of the beams emitted from thelight sources. Moreover, the shading plates 348 prevent the lightdiffused by the diffusion plates 347 from being directly incident uponthe data reading area 36.

Thus, the illumination beams are made incident upon the data readingarea 36 through gaps formed below the shading plates 348. The gaps alsodefine the emission portions 307 through which the illumination beamsare emitted from the lighting apparatus 430. Since the emission portions307 are disposed close to the reference surface 37 of the data readingarea 36, the incident angle β of the bests incident upon the datareading area 36 (i.e., the angle of the optical axes of the beams withrespect to the normal lines to the reference surface 37 of the datareading area 36) can be increased to some extent, so that no image ofthe light sources can be formed on the CCD 43. The increase in theincident angle β also contributes to a uniform illumination of thesymbol data reading area 36. The incident angle β is selected to beapproximately 30° to 60°, and preferably, 40° to 50°.

In particular, the incident points of the beams emitted from the lightsources 341 upon the reference surface of the date reading area 36,i.e., the center points P of illumination are preferably located at adistance of 0.1 to 0.34 times the length of the sides (minor sides) ofthe data reading area perpendicular to the major sides thereof, from themajor sides. If the distance is within the range of 0.1 to 0.34 timesthe length of the minor sides, a more uniform luminance can be obtainedover the whole data reading area.

When the surfaces of the shading plates 348 that face the correspondingmirrors 346 are mirror surfaces, as shown in FIG. 19, the diffusionrange of the beams emitted from the light sources 341 is expanded, sothat a larger area of the reference surface can be uniformlyilluminated. For instance, the beam (optical axis) indicated at 391 inFIG. 19 is reflected by the mirror surface of the shading plate 348 andis then reflected by the mirror 346 to reach the vicinity of the centerportion of the reference surface 37. Hence, the beams emitted from thelight sources 341 can be effectively utilized as illumination light.Alternatively, the reflecting surfaces of the mirrors 346 and the mirrorsurfaces of the shading plates 348 can be replaced with diffusablereflecting surfaces.

In the illustrated embodiment, the light sources 341 have asubstantially identical luminance and the directional (i.e.,orientation) property thereof is shown in FIG. 6.

In the arrangement as discussed above, the angle α defined by theoptical axis of the beams incident upon the CCD 43, and accordingly, thenormal line O to the reference surface 37 and the optical axis of thebeams transmitted through the diffusion plates 347 is approximately 0(α≈0). Namely, the light sources 341 are arranged such that theabove-mentioned two optical axes are substantially parallel with eachother.

With this arrangement, the light sources 341 can be disposed close tothe CCD 43 to realize a compact lighting apparatus 340.

If the light sources 341 are arranged to satisfy the relationship ofα<β, the lighting apparatus 340 and accordingly the data symbol readingapparatus 1 can be made small end compact. The value of α is notnecessarily equal to approximately 0. Namely, the optical axis of thebeams incident upon the CCD 43 and the optical axis of the beamstransmitted through the diffusion plates 347 can be relatively inclined.

Different embodiments of the present invention will be discussed below.

In a ninth embodiment illustrated in FIGS. 20 and 21, the guidingoptical systems is each comprised of a prism 349 which is provided withan incident surface 349a, a reflecting surface 349b, and an emittingsurface 349c. The incident surface 349a is provided with a diffusionplate 347 adhered thereto, that could be identical to the diffusionplate 47 in the first embodiment.

In the embodiments, an incident surface means a plane to which the lightfrom the light source is incident.

The prisms 349 can be made of, for example, plastics, such as acrylicresin or polycarbonate, etc., or various kinds of glasses. Therefractive index of the prisms 349 is preferably 1.4 to 1.6, andpreferably, about 1.5.

The beams emitted from the light sources 341 are transmitted through thediffusion plates 347 and made incident upon the prisms 349 through theincident surfaces 349a. Thereafter, the beams are reflected by thereflecting surfaces 349b and emitted from the emitting surfaces 349c asa first emission light. At the emitting surfaces 349c, a part of thelight is reflected thereby and returned to the inside of the prisms 349.The return beams are then reflected by the reflecting surfaces 349b andemitted through the emitting surfaces 349c as a second emission light.In FIG. 21, the optical axes of the incident beams, the first emissionlight and the second emission light are designated by 392, 393 and 394,respectively.

Due to the function of the prisms, the first emission lights (opticalaxis 393) are made incident upon the data reading area 36 at theportions thereof adjacent to the prisms 349, and the second emissionlights (optical axis 394) reach the opposite edge portions of the datareading area 36 that are located far from the associated prisms 349.Hence, one group of rays emitted from the one prism can be made incidentupon a large area of the data reading area 36 to illuminate therein, sothat a uniform luminance distribution can be obtained within thereference surface 37.

Although the diffusion plates 347 are superimposed on the incidentsurfaces 349a of the prisms 349 in the illustrated embodiment, it ispossible to form the incident surfaces 349a or the emitting surfaces349c of the prisms as diffusable surfaces that constitute the diffusionmeans, in place of the diffusion plates 347. Moreover, the reflectingsurfaces 349b of the prisms 349 can be formed as diffusable surfaces.With this alternative, the number of the components can be reduced andthe manufacturing cost can be minimized.

The upper portion of the emitting surfaces 349c can be subjected to asurface treatment to prevent light from passing through. For example,the upper portions of the emitting surfaces 349c are provided withoptical shading layers coated or evaporated thereon, or optical shadingfilms can be applied applied to make the shading mechanism 349d. Theshading mechanism 349d can be realized for example by a mirror surface,a light absorbing surface, a half mirror, or an optical filter, havingan optional transmittance. In this case, the lower portions of theemitting surfaces 393 on which no shading layer is provided constitutethe emitting portions 307 of the illumination light.

If the shading mechanism is embodied by the mirror surfaces, thenrepetitive reflections of the light occur between the mirror surfacesand the reflecting surfaces 349b, and accordingly, the illuminationlight emitted from the light sources can be effectively utilized toincrease the luminance of the reference surface 37 and enhance theuniformity of the illumination.

Even in case of an absence of the shading mechanism, since the beams(represented by the beam 395) which are incident upon the emittingsurfaces 393 from the inside of the prisms 349 at an angle above thecritical angle are totally reflected by the emitting surfaces, there isno possibility that the light from the light sources 341 can directly beincident upon the reference surface 347, so that the light reflectedthereby reaches the CCD 43, thus leading to a formation of spuriousimages of the light sources. Namely, no direct light along the opticalaxis (beam) 396 occurs.

When the prisms 349 are used as the guiding optical system as mentionedabove, not only can the number of the components be reduced, but alsothe illumination efficiency can be increased to thereby create a moreuniformly illuminated data symbol reading area 39. Note that theinclination angle θ of the mirror 346 and the reflecting surfaces 349bof the prisms 349 is preferably approximately 15° to 30°.

FIG. 22 shows a partial sectional view of a tenth embodiment of thepresent invention. The lighting apparatus 340 shown in FIG. 22 iscomprised of light sources 341, mirrors 371, end prisms 349. The lightsources 341 are provided on an imaginary plane parallel with thereference surface 37, above the CCD 43 to emit the illumination beams ina direction parallel with the reference surface 37. The mirrors 371 arelocated on the optical axes of the illumination beams emitted from therespective light sources 341 to reflect the illumination beams onto theincident surfaces 349a₁ and 349a₂ of the prisms 349. Namely, in theillustrated embodiment, the light guiding optical system is comprised ofthe mirrors 371 and the prisms 349. With this arrangement, the lightingapparatus can be miniaturized.

The guiding optical system is not limited to those in the illustratedembodiments, and can be comprised of, for example, prisms having noreflecting surface, mirrors and prisms in combination, or opticalfibers, etc.

The data reading portion 36 can be of a type in which the beamstransmitted through the reference surface are received and utilized,instead of the beams reflected from the reference surface.

The number of the light sources and the positions of the center pointsof illumination are appropriately varied depending on the size of thedata reading area, the orientation property or luminance of the lightsources, etc.

The present invention is not limited to the illustrated embodiments andcan be equally applied, for example, to a different size of data readingarea. Note that the rectangular data reading area referred to in thisspecification includes a square data reading area.

As can be understood from the above discussion, according to the presentinvention, since the light sources can be positioned close to the datareading portion, a small lighting apparatus can be provided. Moreover,according to the present invention, the data symbol reading area can beuniformly illuminated.

In particular, if there is a shading means provided in the lightingapparatus, the data reading area can be uniformly illuminated with theillumination beams incident thereupon at a large incident angle, whilepreventing the beams emitted by the light sources from being directlyincident upon the data reading area. Furthermore, if there is adiffusion means in the optical paths of the beams emitted from the lightsources, the uniformity illumination can be further enhanced.

(Intentionally Left Blank Below This Line)

The lighting apparatus 440 will be discussed below.

FIG. 25 shows an example of the internal structure of the lightingapparatus 440 and the data reading area 36. FIGS. 26 and 27 show anexample of prism(s) 446 of the lighting apparatus 440. As shown in FIG.25, the lighting apparatus 440 includes a plurality of light sources 441end a pair of prisms 446 located below the light sources 441.

As can be seen in FIG. 24, there are three pairs of light sources 441provided along a pair of opposed parallel sides (e.g., major sides) thatdefine the data (symbol) reading area 36. For clarity, although thefollowing discussion will be addressed to a pair of light sources 441that are opposed with respect to the CCD 43, the discussion can beapplied to the remaining pairs of light sources 441.

Looking at FIG. 25, the CCD 43 is provided with the light receivingsurface perpendicular to the normal line O to the reference surface 37of the data reading area 36 when the lighting apparatus 440 end the datareading area 36 are parallel with the reference surface 37. The parallelarrangement will be referred to as an appropriate state. In theappropriate state, the optical axes of the beams incident upon the CCD43 are parallel with the normal line O. The light sources 441 arearranged such that the optical axes of the principal rays which havebeen emitted from the light sources but have not yet reached the prisms446 are substantially parallel with the normal line O, i.e., the opticalaxis of the light to be received by the CCD 43 (α≈0).

The "principal ray" refers to a ray having the maximum intensity.

As shown in FIG. 25, a pair of prisms 446, 446 are provided on theoptical axes of the light smarted from the respective light sources 441and along the major sides of the rectangular data reading area 36, sothat the emitting surfaces 463 of the prisms 446 are opposed to eachother.

The prisms 446 are each provided with the incident surface 461, thereflecting surface 462, and the emitting surface 463. The emittingsurfaces 463 are provided, on the end portions (upper portions in FIG.25) thereof adjacent to the light sources 441, with shading surfaceportions (light absorbing surfaces) 464.

The incident surfaces 461 are diffusion surfaces which can be formed byrough or irregular surfaces with fine projections and depressions. Theedge of the V-grooves are parallel with each other and to the plane ofthe light reading area.

The prism 446 can be made of plastics, such as acrylic resin orpolycarbonate, or various kinds of glasses. The refractive index of theprisms is approximately 1.4 to 1.6, and preferably close to 1.5.

The prisms 446 are provided on the emitting surfaces 463 thereof with aplurality of continuous grooves 465 which are generally V-shaped in across section and which extend in parallel with the light receivingsurface of the data reading area 36, and accordingly, the lightreceiving surface of the CCD 43. The V-shaped grooves 465 are juxtaposedin a direction perpendicular to the light receiving surface of the CCD43.

Consequently, there is substantially no surface portion perpendicular tothe reference surface 37 in the emitting surfaces 463, except for theend portions 469. Since the groove surfaces 466 and 467 of the V-shapedgrooves 465 provided on the emitting surfaces 463 are all inclined withrespect to the reference surface 37, all the beams emitted from theemitting surfaces 463 onto the reference surface 37 pass through thegroove surfaces 466. If the V-shaped grooves 465 are discontinuouslyprovided on the emitting surfaces 463, the quantity of light passingthrough the groove surfaces 466 of the discontinuous grooves 465 issmaller than the quantity of light passing through the groove surfaces466 of the continuous grooves 465. Therefore, it is preferable that theV-shaped grooves 465 are continuously provided on the emitting surfaces463.

The opposed groove surfaces 466 and 467 of the V-shaped grooves 465 areinclined in opposite directions with respect to the normal line 468 tothe emitting surfaces 463. The inclination angles θ₁ and θ₂ of thegroove surfaces 466 and 467 adjacent to the reference surface 37 and theCCD 43 (light sources 441), respectively, with respect to the normallines 468 to the emitting surfaces 463 are appropriately determined inaccordance with the inclination angle θ₂ of the reflecting surfaces 462of the prisms 446, etc.

If the inclination angle θ₂ of the reflecting surfaces 462 of the prisms46 is 15° to 30°, the inclination anglesθ₁ and θ₂ are 30° to 60°.

The width (pitch) L₁ of the grooves 465 is not limited to a specificvalue, and can be optionally selected in accordance with the size of theprisms 446, etc. In an example, L₁ is approximately 1 to 2 mm.

For the grooves 465 that are located within a predetermined distancefrom the ends (lower ends in FIG. 26) of the prisms 446 adjacent to thereference surface 37, i.e., the grooves 465 contained in a predeterminedzone 495 in the vicinity of the data reading area 36, the groovesurfaces 466 and 467 thereof are diffusion surfaces. The end surfaces469 within the zone 495 are also diffusion surfaces. The diffusionsurfaces are formed, for example, by rough (frosted) or irregularsurfaces with fine projections and depressions.

The zone 495 is closer to the data reading area 36 than the point "A"(intersection point of the optical axis 491 of the principal ray emittedfrom the emitting surface 463 and the groove surface 466) on theemitting surface 463. The width L₂ of the zone 495 is not limited to aspecific value and can be optionally selected in accordance with thesize of the prisms 446 or the inclination angle θ₃, etc. For example, L₂is approximately 2 to 4 mm.

As shown In FIG. 25 there is a protection glass plate 445 between theopposed prisms 446 in the vicinity of the connecting portions of theemitting surfaces 463 and the shading surfaces 464 to prevent a foreignmatter, such as dust from entering the inside of the apparatus.

The operation of the prisms 446 will be described below.

As can be seen in FIG. 25, the beams emitted from the light sources 41are made incident upon the prisms 446 through the incident surfaces 461thereof. Since the incident surfaces 461 are diffusion surfaces, asmentioned above, the incident beams are diffused by the diffusionsurfaces 461 to enter the prisms 446.

The diffusion surfaces 461 contribute to a diffusion of the incidentbeams and an enhancement of the uniformity of the luminance within theillumination desired range value. Note that in FIG. 25, the optical axes491 of the principal rays are indicated by dotted and dashed lines, andspecific rays of the diffused light are indicated by two-dotted anddashed lines, respectively.

The beams incident upon the prisms 46 are reflected by the reflectingsurfaces 462 and emitted from the emitting surfaces 463. The shadingsurfaces 464 prevent the direct beams emitted from the light sources 441or the beams diffused by the diffusion surfaces 461 from being incidentupon the data reading area 36.

Since the emitting surfaces 463 are provided with the V-shaped grooves465, as mentioned above, the beams reflected by the reflecting surfaces462 are made incident upon the groove surfaces 466 of the V-shapedgrooves 465 at right angles or angles approximate thereto, as shown inFIG. 26. Consequently, the beams reflected by the reflecting surfaces462 are made incident upon the reference surface 37 at a smallerincident angle, in comparison with the absence of the grooves 465, sinceno or little refraction of the reflected beams occur when the beams passthrough the groove surfaces 466.

In the illustrated embodiment, since the grooves 465 are formed suchthat the groove surfaces 466 are perpendicular to the optical axes 491of the principal rays reflected by the reflecting surfaces 462, as shownin FIG. 25, the beams on the optical axes 491 travel straight throughthe groove surfaces 466 of the grooves 465 that are located adjacent tothe reference surface 37 toward the data reading area 36. Moreover, thebeams spaced from the optical axes do not travel straight, but arerefracted and emitted from the emitting surfaces 463 at e small angle.

As can be seen in FIG. 26, since the emitting surfaces 463 within thezone 495 are diffusion surfaces, the beams incident upon the groovesurfaces 466 within the zone 495 from the reflecting surfaces 462 arediffused by the emitting surfaces 463 and made incident upon the datareading surface 37.

If there is no groove on the emitting surfaces 463 of the prisms 446, asshown in FIG. 30, the beams reflected by the reflecting surfaces 462 aremade incident upon the emitting surfaces 463 at acute incident angles.Accordingly, the beams are considerably refracted by the emittingsurfaces 463 and made incident upon the data reading area. In comparisonwith the absence of the groove 465, according to the present invention,the incident angle of the beams upon the data reading area 36 (i.e., theangle of the beams with respect to the normal line to the referencesurface 37 of the data reading area 36) can be increased and the beamscan be made incident upon the end portions of the symbol reading area 36adjacent to the prisms 446.

Consequently, if the reference surface 37 is inclined, for example at aninclination angle of +5° or -5°, from the appropriate state, asindicated at 37' in FIG. 30, the beams emitted from the emitting surface463 are reflected within the data reading area 36 and reach the CCD 43,so that spurious images of the light sources can be formed in the CCD43, resulting in an incorrect detection of the data symbols.

According to the present invention, as shown in FIG. 26, since thegrooves 465 are provided on the emitting surfaces 463 of the prisms 446,the incident angle β of the principal rays incident upon the symbol datareading area 36 (i.e., angle of the optical axes 491) of the principalrays with respect to the normal line O to the reference surface 37 ofthe data reading area 36 when the normal line O to the reference surface37 is parallel with the optical axes of the beams to be received by thedata reading area 36, can be increased in comparison with the case wherethere is no groove 465 on the emitting surfaces 463 of the prisms 446.

Consequently, as shown in FIG. 25, if the reference surface 37 isparallel with the data reading portion 404 or even if the referencesurface 37 is inclined with respect to the appropriate state thereof(for example at an inclination angle of +5° or -5°), no spurious imageof the light sources can be formed in the CCD 43. Thus, according to thepresent invention, the data symbols can be correctly read, regardless ofthe state (inclination) of the reference surface 37 of the data readingarea 36.

The increase in the incident angle β contributes to a uniformillumination of the data reading area 36. For example, the incidentangle β is 30° to 60°, preferably, 40° to 50°.

In the data symbol reader 1 according to the present invention, sincethe emitting surfaces of the prisms 446 within the predetermined ranges495 are diffusion surfaces, as mentioned above, the illumination beamswhich would be otherwise concentrated on the end portions of the datareading area can be effectively diffused. Consequently, if the object tobe read has a high reflectivity, the surface of the object (referencesurface 37 of the data reading area 36) can be uniformly illuminated.

In the illustrated embodiment, since the prisms 446 are used as theoptical guide system which deflects the beams emitted from the lightsources 441 in predetermined directions so as to make the same incidentupon the reference surface 37 of the data reading area 36, the number ofthe components can be reduced in comparison with an optical guide systemin which optical elements such as mirrors are employed in combination.

Preferably, the position of the incidence of the principal rays 491 uponthe reference surface 37 of the data reading area 36 is located at adistance of 0.1 to 0.34 times the length of the sides (minor sides) ofthe data reading area perpendicular to the major sides thereof, from themajor sides. If the distance is within 0.1 to 0.34 times the length ofthe minor sides of the data reading area, a more uniform luminance ofthe whole data reading area can be obtained.

The light sources 441 are arranged such that if the normal line O of thereference surface 37 is parallel with the optical axes of the beamsreceived by the data reading portion 4 (i.e., the beams incident uponthe CCD 43), the angle α between the optical axes of the beams receivedby the data reading portion, i.e., the normal line O of the referencesurface 37 and the optical axes 491 of the principal rays emitted fromthe light sources 441 but not reaching the prisms 446 is nearly equal to0 (α≈0). In other words, the optical axes of the beams received by thedata reading portion are substantially parallel with the optical axes491 of the principal rays.

With this arrangement, the light sources 441 can be provided close tothe CCD 43, resulting in a small and compact lighting apparatus 440.

In the present invention, preferably α<β, as mentioned above. The shapeof the prisms 346, and accordingly, the angles and positionalrelationship of the incident surfaces 461, the reflecting surfaces 462,and the emitting surfaces 463 (groove surfaces) of the prisms 446, andthe positional relationship between the prisms 446 and the light sources441 are appropriately determined to satisfy α<β. If α<β, the lightingapparatus 440 and the data symbol reader can be miniaturized. Note thatα is not necessarily equal to or nearly equal to zero.

The present invention is not limited to the illustrated embodiments, Forinstance, although the groove surfaces 466 and 467 of the grooves 465within the ranges 495 of the emitting surfaces 463 of the prisms 46 arediffusion surfaces, it is possible to provide the diffusion surfacesonly on the groove surfaces 466 adjacent to the reference surface 37.

Moreover, it is possible to provide no diffusion surfaces on theemitting surfaces 463 (groove surfaces 466 and 467).

Although the incident surfaces 461 of the prisms 46 are diffusionsurfaces in the illustrated embodiments, it is possible to provide theincident surfaces 461 that are not diffusion surfaces. In thisalternative, diffusion plates are adhered to or disposed in front of theincident surfaces 461 of the prisms 446 at a predetermined distance.

The reflecting surfaces 462 and the shading surfaces 463 of the prisms446 can be replaced with reflecting plates and shading plates,respectively.

The shading surfaces 463 of the prisms 446 are not limited to lightabsorbing surfaces as in the above-mentioned embodiments, and can be forexample reflecting surfaces (mirror surfaces), half mirrors, or opticalfilters, etc. The transmitance of these optical elements can beoptionally selected.

The grooves 465 of the prisms 46 are identical in shape, width, pitchand inclination angles (θ₁, θ₂), etc., in the illustrated embodiments.However, the grooves 465 can be different in the direction of the linenormal to the light receiving surface of the CCD 43 (i.e., in thedirection of the optical axes of the principal rays before reaching theprisms 446).

The data reading portion 4 can be of a type in which the beamstransmitted through the reference surface 37 are received and utilized,instead of the beams reflected from the reference surface.

The number of the light sources and the positions of the center pointsof illumination are appropriately varied depending on the size of thedata reading area, the orientation property or luminance of the lightsources, etc.

The present invention is not limited to the illustrated embodiments andcan be equally applied, for example, to a different size of data readingarea. Note that the rectangular data reading area referred to in thisspecification includes a square data reading area.

Several examples of the luminance distribution will be discussed below.

The luminance distributions of the data reading area 36 in thehorizontal direction (minor side direction) were measured using thelighting apparatus 440 shown In FIG. 25. The six light emitting diodesused as the light sources were identical to each other. The orientationproperty thereof is shown in FIG. 6. The size of the data reading area36 was as follows; Lx=18.5 mm and Ly=24.5 mm.

Other experimental conditions in the examples were described below.

FIGS. 28 and 29 show examples of luminance distribution of the datareading area 36 (FIG. 25) in the horizontal direction (minor sidedirection), using the prisms whose conditions were described below. InFIGS. 28 and 29, the ordinate represents the level of the video signals(unit: IRE), and the abscissa represents the position of theillumination points in the horizontal direction. The curves "a₁ " and"a₂ " designate the luminance distributions when a subject to be read isa highly diffusing paper, and the curves "b₁ " and "b₂ " designate theluminance distributions when a subject to be read is a highly reflectivepaper. It should be appreciated that the degree of the uniformityincreases as the curves was "a₁ ", "a₂ ", "b₁ ", and "b₂ " are asapproximate to straight as possible.

EXAMPLE 11:

The prisms used were as follows. The emitting surfaces of the prismswere not the diffusion surfaces.

Material of the prisms: Acrylic resin (refractive index=1.5)

Width L₁ of the grooves: 1 mm

Angle θ₁ : 45°

Angle θ₂ : 35°

Angle θ₃ : 22.5°

Angle α: 0°

Angle β: 45°

The results are shown in FIG. 28.

EXAMPLE 12:

In the prisms used, the groove surfaces 466 and 467 and the end surfaces469 within the range 495 of the emitting surfaces of were diffusionsurfaces. Other requirements of the prisms were identical to those inexample 11 mentioned above.

Width L₂ of the range 495: 4 mm

The results are shown in FIG. 29.

As can be seen from the experimental results shown in FIG. 28, inexample 11 in which the emitting surfaces of the prisms were not thediffusion surfaces, the highly diffusing paper could be uniformlyilluminated over the whole data reading area 39. Even in the case of thehighly reflective paper, a uniform illumination thereof could beachieved except for the end portions of the data reading area 39.

Also, as may be seen from the experimental results shown in FIG. 29, inexample 12 in which the emitting surfaces of the prisms within the range495 thereof were the diffusion surfaces, not only the highly diffusingpaper but also the highly reflective paper could be uniformlyilluminated over the whole data reading area 39.

As can be understood from the foregoing, according to the presentinvention, since the light sources can be located close to the datareading area, a small lighting apparatus which uniformly illuminates thesymbol reading area can be obtained.

Regardless of the state of the reference surface of the data readingarea, that is, if the reference surface is parallel with or inclinedwith respect to the data reading portion, no direct entrance of thereflected light into the data reading portion takes place, so that datacan be correctly read without the need for a precise adjustment orpositioning of the illumination light in the horizontal direction withrespect to the reference surface.

Furthermore, if the portions of the emitting surfaces of the prisms inthe vicinity of the data reading area are diffusion surfaces, the datasymbol reading area can be uniformly illuminated, regardless of thecharacteristics (reflection or diffusion characteristics) of the objectto be read. Consequently, the symbol reading areas of variouscharacteristics of objects can be correctly read or detected.

We claim:
 1. A lighting apparatus which illuminates a two dimensionaldata reading area for a data reader, comprising:a plurality of lightsources arranged to define rows extending along each of one pair ofopposing sides of said two dimensional data reading area; an opticalaxis for each said light source being inclined at a predeterminedinclination angle with respect to a line normal to a reference surfaceof said two dimensional data reading area.
 2. The lighting apparatusaccording to claim 1, said light sources defining each of said rowshaving substantially parallel optical axes.
 3. The lighting apparatusaccording to claim 1, said predetermined inclination angle being equalfor each of said plurality of light sources defining each of said rows.4. The lighting apparatus according to claim 1, said light sourcesemitting beams of light, said light sources positioned such that opticalaxes of said light beams emitted from said light sources form a twodimensional array in a plane parallel to said reference surface.
 5. Alighting apparatus which illuminates a two dimensional data reading areafor a data reader, comprising:a plurality of light sources arranged todefine rows extending along each of a first pair of opposing sides ofsaid two dimensional data reading area; an optical axis of said lightrays emitted from each said light source being inclined at apredetermined inclination angle with respect to a line normal to areference surface which includes said two dimensional data reading area;said optical axes of light rays emitted from said light sources ontosaid reference surface being spaced from each of said first pair ofopposing sides of said two dimensional data reading area by a distancewithin a range of 0.1 to 0.34 times a length of an other pair ofopposing sides of said two dimensional data reading area.
 6. A lightingapparatus according to claim 5, wherein said predetermined inclinationangle of said optical axes with respect to said line normal to saidreference surface is inclined 30° to 60°.
 7. A lighting apparatusaccording to claim 5 wherein said first pair of opposing sides of saidtwo dimensional data reading area are major sides.
 8. A lightingapparatus according to claim 5, wherein said light sources arrangedalong said first pair of opposing sides are symmetrical with respect toa center of said data reading area.
 9. A lighting apparatus according toclaim 5, wherein said two dimensional data reading area is in a form ofa rectangle.
 10. A lighting apparatus according to claim 5, wherein saidtwo dimensional data reading area is in the form of a pattern of blackand white segments in a matrix arrangement.
 11. The lighting apparatusaccording to claim 5, said light sources defining each of said rowshaving substantially parallel optical axes.
 12. The lighting apparatusaccording to claim 5, said predetermined inclination angle being equalfor each of said plurality of light sources defining each of said rows.13. The lighting apparatus according to claim 5, said light sourcesemitting beams of light, said light sources positioned such that opticalaxes of said light beams emitted from said light sources form a twodimensional array in a plane parallel to said reference surface.
 14. Alighting apparatus which illuminates a rectangular data reading area fora data reader, comprising:a plurality of light sources arranged todefine rows extending along each of a pair of opposing sides of saidrectangular data reading area and which emit light beams to illuminatesaid rectangular data reading area; and, an adjuster for each said lightsource which adjusts a illuminance of each of said light sources at acenter point of illumination of said light source incident on areference surface which includes said rectangular data reading area touniformly illuminate said rectangular data reading area.
 15. A lightingapparatus according to claim 14, wherein said adjusters adjust adistance between said light sources and said center points ofillumination on said reference surface.
 16. A lighting apparatusaccording to claim 14, wherein said adjuster for each said light sourceis in the form of an optical diffuser.
 17. A lighting apparatusaccording to claim 14, wherein said adjuster for each said light sourceis a beam attenuator.
 18. A lighting apparatus according to claim 14,wherein said optical axis of each said light source is inclined at apredetermined inclination angle with respect to said reference surfaceof said rectangular data reading area, and wherein said optical axis ofeach said light source which is incident on said reference surface isspaced from said one pair of opposing sides of said rectangular datareading area by a distance within a range of 0.1 to 0.34 times a lengthof an other pair of opposing sides of said rectangular data readingarea.
 19. A lighting apparatus according to claim 14, wherein saidluminance of said light sources at said center points of illuminationare adjusted such that the outermost of said light sources with respectto a center of said rectangular area have a higher luminance withrespect to the other said light sources.
 20. The lighting apparatusaccording to claim 14, said light sources defining each of said rowshaving substantially parallel optical axes.
 21. The lighting apparatusaccording to claim 18, said predetermined inclination angle being equalfor each of said plurality of light sources defining each of said rows.22. The lighting apparatus according to claim 14, said light sourcesemitting beams of light, said light sources positioned such that opticalaxes of said light beams emitted from said light sources form a twodimensional array in a plane parallel to said reference surface.